This invention relates generally to a parking brake for a rail vehicle braking system, and more particularly to a brake cylinder parking brake which can automatically lock the brakes on the rail vehicle in an applied position responsive to a brake application. The brake cylinder parking brake can be configured for use on both truck and car mounted rail car brake systems.
As is generally well known in the rail industry, when rail cars are taken out of a train and parked at a siding or yard, the hand brake or parking brake on at least some of these cars is applied as a precaution against unwanted or unexpected movement of the cars. A typical rail car hand brake system normally consists of an apparatus for manually applying and biasing one or more brake shoes against the tread of one or more wheels of the rail car by either turning a hand wheel or pumping a ratchet handle on a hand brake mechanism attached to the rail car.
In both truck and car mounted rail car braking systems (illustrated in FIGS. 1-3), the hand brake mechanism is usually either a cast or stamped metal gear housing, and is typically attached to an outside end wall of the rail car. A rotatable chain drum must be rotated by turning the hand wheel to wind a brake chain onto the chain drum. The other end of the brake chain normally extends through the bottom of the gear housing and is interconnected with cable or other linkage, such as a hand brake lever, to the brake beams which carry the brake shoes. The winding of the brake chain onto the chain drum applies tension to the brake chain and brake linkage to draw the brake shoes against the tread surfaces of adjacent rail car wheels and, accordingly, applies the hand brake as intended.
A disadvantage of this prior art type hand brake arrangement is that train operators must manually apply the parking brake on each of dozens, or even hundreds, of rail cars, which requires a considerable amount of time and labor. Additionally, the operators must be certain that the hand wheel is turned a sufficient amount to ensure that the parking brake is engaged. The possibility also exists that an operator may forget to apply the brake altogether on a rail car, which could result in unexpected movement of the rail car while parked at the siding or yard. Alternatively, wheel damage can result due to a failure to release the handbrake from the applied position before the train resumes movement. Operation of the hand wheel also requires exerting a considerable amount of physical force from an awkward position, which makes the hand brake difficult to apply. Injuries to operators also sometimes occur related to hand brake use. Furthermore, since brake cylinder pressure can leak over time, a potentially hazardous condition can develop if a loss of brake cylinder pressure occurs subsequent to an emergency brake application, and particularly if the train is stopped on a grade.
A loaded brake engagement mechanism has been used in Type AB-8 and AB-10 Manual Empty and Load Freight Car Brake Equipments, manufactured By Westinghouse Air Brake Technologies, Inc., the assignee of the present invention. As described in Instruction Pamphlet 5062-2Sup. 1, dated May 1942, this mechanism incorporated a telescoping housing and push rod arrangement inside a specially designed “UL” type brake cylinder, called a “load brake cylinder” which was used to make a loaded brake application. The load brake cylinder was one of two separate brake cylinders on the rail vehicle, the other being an “empty brake cylinder”, which where used to control the application of brakes on the rail vehicle. The piston push rods of each brake cylinder were connected to a common lever, called the live cylinder lever, which was connected to the brake rigging on the rail car. In the load brake cylinder, the push rod telescoped within a hollow tube, or housing, and the relationship between the housing and the push rod was regulated by a ratcheting mechanism which cooperated with notches in the push rod. During a loaded brake application, the empty brake cylinder would operate and, via the connection of the push rods of both the empty and load brake cylinders to the live brake cylinder lever, the push rod of the load brake cylinder would extend along with the push rod of the empty brake cylinder. The ratcheting mechanism cooperated with the notches on the push rod of the load brake cylinder such that as it extended, i.e., telescoped, out from the housing, it would be blocked from retracting into the housing. When the empty brake cylinder reached maximum extension of the push rod, the load brake cylinder could be pressurized which caused the housing to extend. Since the ratcheting mechanism had locked the push rod in its telescoped position relative to the housing, the push rod was caused to further extend an additional amount along with the housing, thereby increasing the braking force. Basically, the telescoping function of the push rod with respect to the housing, controlled via the ratcheting mechanism, permitted a longer piston stroke in a more compact manner. However, the ratcheting mechanism only blocked the push rod from retracting within the housing itself. The ratcheting mechanism did not block the housing from retracting, and carrying the push rod long with it, which released the brakes.
Some embodiments of a rail vehicle parking brake which is adapted to address such disadvantages of conventional rail vehicle parking brakes are described in copending U.S. Provisional Application Ser. No. 60/501,383, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference.
Additionally, further embodiments of a parking brake for a rail vehicle which can be applied automatically to lock the brakes on the rail vehicle are disclosed hereinafter.